Why is cyclic dominance so rare?

Abstract

Natural populations can contain multiple types of coexisting individuals. How does natural selection maintain such diversity within and across populations? A popular theoretical basis for the maintenance of diversity is cyclic dominance, illustrated by the rock-paper-scissor game. However, it appears difficult to find cyclic dominance in nature. Why is this case? Focusing on continuously produced novel mutations, we theoretically addressed the rareness of cyclic dominance. We developed a model of an evolving population and studied the formation of cyclic dominance. Our results showed that the chance for cyclic dominance to emerge is lower when the newly introduced type is similar to existing types, whereas the introduction of an unrelated type improves these chances.This suggests that cyclic dominance is more likely to evolve through the assembly of unrelated types whereas it rarely evolves within a community of similar types. * traulsen@evolbio.mpg.de U. stansburiana and D. melanogaster, whereas common resource competition induces cyclic dominance between species.However, traditional theoretical work assumes a set of predefined cyclic dominance types without asking how they developed or came together. In ecosystems, the introduction of a new species through migration can lead to such cyclic dominance. However, immigrating species can also disturb and destroy cyclic dominance. In evolving populations, new types can arise through mutation and recombination. In the same manner, mutation and recombination can lead to the formation of cyclic dominance but can also lead to types that do not fit into such types of dominance and break the cycle. A recent experimental study [27] indicated that in the assembly of microbial ecosystems found in one grain, only 3 of almost 1000 triplets exhibited cyclic dominance, whereas more than 500 exhibited non-cyclic dominance triplets. Other soil bacterial species [28,29] also displayed a lack of cyclic dominance.This rareness is present in both soil bacteria and plant systems [24]. Why is it so difficult for cyclic dominance to assemble or evolve? In this study, we ask the following question theoretically: How frequent is cyclic dominance in situations in which new types constantly arise, providing an opportunity for new cycles but also breaking old cycles at the same time?Forming a cyclic dominance from a single type is challenging because any pair has a dominance relationship. Once a new mutant emerges in a homogeneous population, one of the types quickly vanishes because of the dominance. Therefore, a third type must arise before the population loses either of the two previous types. Such a precise timing of the arrival of a new type is critical for developing cyclic dominance and it can occur when new types arise at a high frequency, either through high mutation rates, recombination, or immigration [30,31]. This rapid evolution can be achieved through both high mutation rates per capita and large population sizes [30][31][32][33][34]. Thus, we considered a model in which the popu...

Higher-order effects, continuous species interactions, and trait evolution shape microbial spatial dynamics

“…Despite its prominence in modeling studies, pure cyclic dominance, in which there is a "closed" loop of dominance, is rare in nature (39)(40)(41)(42). In contrast, rapid evolution routinely leads to model systems featuring semicyclic or noncyclic patterns in which higher-order interactions, such as those involving antibioticproducing, sensitive, and resistant species, are common (35,40).…”

“…Despite its prominence in modeling studies, pure cyclic dominance, in which there is a "closed" loop of dominance, is rare in nature (39)(40)(41)(42). In contrast, rapid evolution routinely leads to model systems featuring semicyclic or noncyclic patterns in which higher-order interactions, such as those involving antibioticproducing, sensitive, and resistant species, are common (35,40). Therefore, the notion of pure cyclic dominance used in earlier studies of antagonistic microbial dynamics needs to be supplemented with evolving, "mixed" patterns of dominance in order to better model microbial community interactions.…”

Higher-order effects, continuous species interactions, and trait evolution shape microbial spatial dynamics

“…Such studies have focused instead on detailed understanding of a small number of discrete species under a low mutation regime (47). Recently, studies have focused on understanding the effects of high mutational regimes in community assembly, which better represent microbial systems (38), and can generate frequent non-cyclic interactions (40). Our efforts have considered an array of mutational regimes and characterized the importance of non-cyclic patterns of interactions in the assembly and maintenance of microbial communities.…”

“…Scaling up analytic models of cyclic dominance to species-rich scenarios is not possible because the incorporation of more than a few discrete species makes the dynamics extremely complex and hard to interpret using equation-based approaches (20). Despite its prominence in modeling studies, pure cyclic dominance, in which there is a 'closed' loop of dominance, is rare in nature (39)(40)(41)(42). In contrast, rapid evolution routinely leads to model systems featuring semi-cyclic or non-cyclic patterns in which higher-order interactions, such those involving antibiotic producing, sensitive, and resistant species, are common (35,40).…”

“…Despite its prominence in modeling studies, pure cyclic dominance, in which there is a 'closed' loop of dominance, is rare in nature (39)(40)(41)(42). In contrast, rapid evolution routinely leads to model systems featuring semi-cyclic or non-cyclic patterns in which higher-order interactions, such those involving antibiotic producing, sensitive, and resistant species, are common (35,40). Therefore, the notion of pure cyclic dominance used in earlier studies of antagonistic microbial dynamics needs to be supplemented with evolving, 'mixed' patterns of dominance, in order to better model microbial community interactions.…”